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New problems casting silver, centrifugal.
Daverham - Monday, March 1, 2010 - 1:49amCasting casting | centrifugal | jewelry | silver
In years past, I have cast some silver and gold jewelry successfully, techniques and equipment that are FAR from "by-the-book". Until this week, I had never used a vacuum de-bubbler. My burnout oven was a metal coffee can on top of a hotplate that surely never reached so much as 700 deg F (flask never glowed orange). And my centrifugal caster appears to be home-made (I bought it used), and only spins for about 30 seconds. With all this... I have cast some pretty nice stuff. But I'm trying to do better. So...
I made a vacuum de-bubbler and it really sucks the bubbles out of my investment. I bought a small burnout oven that hits 1200 deg F in 45 minutes and really makes that flask glow orange hot! I bought a nice, clean new crucible, and glazed it with Borax. All should be in order.... but my castings are having huge flaws for the first time ever. It seems to me that the metal might be flowing back out of the mold/sprue because the centrifuge doesn't spin long enough. Does that seem possible to anyone?
I melt the silver, release the centrifuge and it spins.... everything looks perfect, the metal was measured perfectly... no slop. Then, as the centrifuge starts to slow - PLOP - a glowing, red, blob of molten silver drops to the ground, and my casting looks like the one in the picture below. Also see the drip mark on the mold.
For the first time, I'm setting that flask/mold on the centrifuge glowing red hot, right out of the kiln... is that TOO hot? The metal isn't freezing fast enough? Or that is a good thing, but it needs to spin longer? At this point, it seems like just pouring it in there would do the trick. I can't afford an $800 vacuum casting machine, but given the ease with which I made a vacuum de-bubbler, that seems like something I could do as well. Thanks for any advice!
That big, ugly flaw is right where the sprue attached
More of my pics: http://www.flickr.com/photos/11168745@N06/